Antibiotics and Blood Pressure Pills will Kill You?

Nov 18, 2013

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

Ahhh. Time Keeping. Great seats . for a price. Have you ever wanted to get down to ice level at your childs hockey game, but didnt have the skills to be behind the bench? Have you ever wanted to talk directly to the refs? Do I have a deal for you! For the low, low price of a good nights sleep, you too could be a time keeper! Dont get me wrong, it is not difficult to run the time clock. All minor hockey teams are always looking for parents to volunteer to run it. And you should. It is just hitting a couple buttons to change the score and flipping a switch to start and stop the clock. It is easy. You will be way better at it than I am. And if you do it, I can stop periodically waking up in the middle of the night in a cold sweat because I can hear a whole rink is yelling at me to turn on the clock.


My neurotic time keeping nightmares arent the only things yelling at me lately. I ran across a CTV news article that yelled Interaction between hypertension drug and antibiotic can lead to kidney injury. That caught my attention. Obviously drugs in the news interest me and headlines like that usually generate a whole bunch of phone calls to me in the pharmacy. I looked up and read the original article. Gandhi et. al published an article in JAMA online in November that looked at the interaction between a common antibiotic and a common blood pressure pill. And the researchers did find an increased chance of kidney and blood pressure problems. Spoiler alert! Despite the headlines on CTV, the chance of problems were small.


Lets look at the study first. The researchers looked at about 190,000 older people in Ontario who were taking antibiotics called macrolides and blood pressure pills called calcium channel blockers together. This wasnt a gold standard double blind placebo controlled trial. The researchers looked back on the health records of these people with an average age of 76 from 2003 through 2012. About half were prescribed the macrolide antibiotic clarithromycin (n = 96 226) and about half were on the macrolide antibiotic azithromycin (n = 94 083). All the subjects were also on a calcium-channel blocker (amlodipine, felodipine, nifedipine, diltiazem, or verapamil) for blood pressure.


The researchers picked the antibiotics azithromycin and clarithromycin is because they are similar antibiotics and would be used to treat similar infections. However, clarithromycin is more likely to affect the enzymes that break down calcium channel blockers than azithromycin. That means someone on clarithromycin and a calcium channel blocker together might end up with way more of the blood pressure pill in their systems than normal. This could lead to dangerously low blood pressures and/or kidney damage.


The studys primary endpoint was people who were hospitalized with acute kidney injury within 30 days of being on the antibiotic/blood pressure pill combination. The researchers found people on the calcium channel blocker amlodipine and the antibiotic clarithromycin ended up in hospital with acute kidney injury more often than people on amlodipine and azithromycin. But the numbers were very, very small. 420 patients of 96 226 taking clarithromycin or 0.44% got kidney damage vs 208 patients of 94 083 taking azithromycin or 0.22%. These are tiny risks. And because this is a retrospective study based on how doctors entered billing codes into a database, we dont know for certain that a drug interaction caused the kidney damage. Although unlikely, we cant tell if there were other causes of the kidney damage.


Lets look more closely at the actual quoted risks. National Geographic lists the lifetime risk of being hit by lightning as 1 in 3000. That is a 0.03% risk. Your odds of dying in a car crash are about 1 in 100 or a 1% risk. The absolute increase in risk between these two antibiotics when used with amlodipine was 0.22%. So the chances of this interaction affecting your kidneys if you take the clarithromycin and amlodipine together are greater than getting hit by lightning, but less than dying in a car crash.


This is a good study and has added to our knowledge of which drugs not to mix together. More care should be taken by doctors and pharmacists to not combine calcium channel blockers and clarithromycin. But the chances of harm to the patient are very small. If you have ever been on clarithromycin and amlodipine together, you dont need to lose any sleep over it. Now if I just dont screw up my next turn in the time box, maybe dreams wont be filled with people yelling START THE CLOCK!



The information in this article is intended as a helpful guide only. It is not intended to be used as a substitute for professional advice. If you have any questions about your medications and what is right for you see your doctor, pharmacist or other health care professional.


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JAMA article -

The Odds of Dying -

National Geographic Flash Facts on Lightning -

CTV news on clarithromycin and amlodipine -


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